Enable Gather with negative indices. (#3701)

* Enable Gather with negative indices.

* Address PR feedback.

* Remove GOE from Gather unit tests.

src/ngraph/runtime/cpu/kernel/gather.hpp

@@ -69,6 +69,8 @@ namespace ngraph
                     Eigen::array<Eigen::Index, Rank1> in_dims;
                     Eigen::array<Eigen::Index, Rank2> out_dims;
 
+                    auto axis_length = inputs_shape[axis];
+
                     for (int i = 0; i < Rank1; i++)
                     {
                         in_dims[i] = inputs_shape[i];
@@ -84,6 +86,7 @@ namespace ngraph
                         static_cast<ElementType*>(inputs), in_dims);
 
                     auto indices_ptr = static_cast<IndicesType*>(indices);
+                    IndicesType index_value;
                     auto indices_rank = indices_shape.size();
                     auto outer_loop_num = 1;
                     for (int i = 0; i < axis; i++)
@@ -123,7 +126,10 @@ namespace ngraph
                             // at axis
                             in_extents[axis] = 1;
                             // at axis, get the value from indices arg
-                            in_offsets[axis] = indices_ptr[0];
+                            index_value = indices_ptr[0];
+                            // take care of negative indices
+                            in_offsets[axis] =
+                                index_value >= 0 ? index_value : index_value + axis_length;
 
                             // before axis
                             for (int r = 0; r < axis; r++)
@@ -193,7 +199,10 @@ namespace ngraph
                             }
                             // at axis, get the value from indices arg
                             int k = i % num_indices;
-                            in_offsets[axis] = indices_ptr[k];
+                            index_value = indices_ptr[k];
+                            // take care of negative indices
+                            in_offsets[axis] =
+                                index_value >= 0 ? index_value : index_value + axis_length;
 
                             // indices_from_indices_arg depends on indices_shape and k.
                             // suppose the inputs has shape {3, 3, 3}, indices has shape {2, 2}, and

src/ngraph/runtime/intelgpu/unit_test.manifest

@@ -64,6 +64,7 @@ gather_2d_indices_axis_1_2d_input
 gather_scalar_indices_no_axis_2d_input
 gather_1d_indices_no_axis_1d_input
 gather_2d_indices_no_axis_2d_input
+gather_2d_negative_and_positive_indices_no_axis_2d_input
 gather_3d_indices_no_axis_2d_input
 gather_4d_indices_no_axis_2d_input
 gemm

src/ngraph/runtime/plaidml/unit_test.manifest

@@ -196,6 +196,7 @@ gather_4d_indices_no_axis_uint8
 gather_4d_indices_no_axis_2d_input
 gather_3d_indices_no_axis_2d_input
 gather_2d_indices_no_axis_2d_input
+gather_2d_negative_and_positive_indices_no_axis_2d_input
 gather_1d_indices_no_axis_1d_input
 gather_scalar_indices_no_axis_2d_input
 gather_2d_indices_axis_1_2d_input

src/ngraph/runtime/reference/gather_nd.hpp

@@ -83,6 +83,8 @@ namespace ngraph
                     for (size_t i = 0; i < slice_rank; i++)
                     {
                         U index = indices[indices_index];
+                        // take care of negative indices
+                        index = index >= 0 ? index : index + params_shape[i];
                         params_start_corner[i] = index;
                         params_end_corner[i] = index + 1;
                         indices_index++;